t.w.microdom : module documentation

This is an implementation of what we consider to be the useful subset of
the DOM. The chief advantage of this library is that, not being burdened
with standards compliance, it can remain very stable between versions. We
can also implement utility 'pythonic' ways to access and mutate the XML
tree.

Since this has not subjected to a serious trial by fire, it is not
recommended to use this outside of Twisted applications. However, it seems
to work just fine for the documentation generator, which parses a fairly
representative sample of XML.